Signal transduction pathways are made up of growth factors, their receptors, upstream regulators of the growth factors, and downstream intracellular kinase networks. These pathways regulate many cellular processes, including proliferation, and appear to play a key role in oncogenesis.
The epidermal growth factor receptor (EGFR) and its pathway members are among the most widely explored signaling pathways. Signaling through this pathway elicits diverse biological responses whose manifestations can include mitogenesis or apoptosis, enhanced cell motility, protein secretion, and differentiation or dedifferentiation. Up-regulated EGFR signaling has been implicated in organ morphogenesis, maintenance and repair, and is correlated with invasion and metastasis of many types of tumors. Thus, EGFR and its pathway signaling members are targets for therapeutic intervention in wound repair and cancer.
Signal transduction pathways, such as the EGFR pathway, are evolutionarily conserved among species as distant as the worm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and vertebrates (Duffy J B, and Perrimon N, Curr. Opin. Cell Biol. (1996) 8:231-238). In fact, ligands for the Drosophila EGFR (DER), known as Spitz (Rutledge B, et al, Genes Dev. (1992) 6:1503-1517) and Gurken (Neuman-Silberberg F S, and Schupbach T, Cell (1993) 75:165-174), are both similar to TGFα (transforming growth factor alpha), the ligand for the vertebrate EGFR (Massaque J, J Biol Chem. (1990) 265:21393-21396). The rhomboid gene, which encodes a transmembrane protein, is another upstream member of this pathway (Bier E., et al., Genes Dev. (1990) 4:190-203). In Drosophila, rhomboid protein transforms Spitz from a membrane-bound to a secreted form, and thus triggers and upregulates the DER signaling pathway (Wasserman J D et al, Genes Devel (2000) 14:1651-1663). DNA sequences related to rhomboid have been identified in C. elegans (Wasserman J D, and Freeman M, Trends Cell Biol (1997) 7:431-436), and in mammals (Pascall J C, and Brown K D, FEBS letters (1998) 429:337-340; human: GI#3287191 and GI#7020534, among others; rat: GI#3297936; ), suggesting that rhomboid function may be evolutionarily conserved. Modulating signal transduction pathway activity involved in tumor growth and development is essential in understanding the development of many cancers, and eventually, for the treatment of cancer.
The ability to screen or manipulate the genomes of model organisms such as Drosophila provides a powerful means to analyze biochemical processes that, due to significant evolutionary conservation, have direct relevance to more complex vertebrate organisms. Due to high level of gene and pathway conservation, the strong similarity of cellular processes, and the functional conservation of genes between Drosophila and mammals, identification of novel genes involved in particular pathways and their functions in flies can directly contribute to the understanding of the correlative pathways and methods of modulating them in mammals (Mechler B M et al., 1985 EMBO J 4:1551-1557; Gateff E. 1982 Adv. Cancer Res. 37: 33-74; Watson K L., et al., 1994 J Cell Sci. 18: 19-33; Miklos G L, and Rubin G M. 1996 Cell 86:521-529; Wassarman D A, et al., 1995 Curr Opin Gen Dev 5: 44-50; Booth D R. 1999 Cancer Metastasis Rev. 18: 261-284). For example, a genetic screen can be carried out in Drosophila in which a gene of interest is overexpressed, resulting in a visible phenotype; a cross is made with flies having mutations in other genes; and progeny are identified that have an enhancement or reduction of the original overexpression phenotype, indicating that the mutated gene is a “modifier” involved in the same or overlapping pathway as the gene of interest (Rorth P., et al., Development (1998) 125:1049-1057; WO0015843). When the gene of interest is an ortholog of a human gene implicated in a disease pathway, such as a tumor suppressor gene or oncogene, modifier genes can be identified that may be attractive candidate targets for novel therapeutics.